SummaryProtein kinase C (PKC) is a heterogeneous family of serine ⁄ ⁄ threonine protein kinases that have different biological effects in normal and neoplastic melanocytes (MCs). To explore the mechanism behind their differential response to PKC activation, we analyzed the expression profile of all nine PKC isoforms in normal human MCs, HPV16 E6 ⁄ ⁄ E7 immortalized MCs, and a panel of melanoma cell lines. We found reduced PKCb and increased PKCf and PKCi expression at both the protein and mRNA levels in immortalized MCs and melanoma lines. We focused on PKCb as it has been functionally linked to melanin production and oxidative stress response. Re-expression of PKCb in melanoma cells inhibited colony formation in soft agar, indicating that PKCb loss in melanoma is important for melanoma growth. PKCbII, but not PKCbI, was localized to the mitochondria, and inhibition of PKCb significantly reduced UV-induced reactive oxygen species (ROS) in MCs with high PKCb expression. Thus alterations in PKCb expression in melanoma contribute to their neoplastic phenotype, possibly by reducing oxidative stress, and may constitute a selective therapeutic target.